The present invention relates generally to portable or hand bicycle pumps.
U.S. Pat. No. 3,907,041, issued on Sept. 23, 1975, assigned to the assignee of the present application, describes a hand bicycle pump equipped with means adapted to indicate the pressure in the tire in the course of inflation.
This means is accommodated in a longitudinal cylindrical boss integral with the parallel to the pump body and essentially comprises a piston having a graduated scale displaceable in a viewing window in response to the pressure present inside the tire with which it is in communication.
In the assignee's French Printed Patent Application No. 2,271,417 published on Dec. 12, 1975, there was proposed a hand pump of the aforesaid type, however, in this pump one end of the pump piston rod carrying the compression piston is provided with a hand grip having a connector adapted for an inflation valve so that during inflation the pump body is reciprocated along the pump piston rod. In this construction the pressure indicator is housed inside the compression piston rod.
In the two cases just briefly described the pump provides an indication of the pressure inside the tire. Hence in these two types of pump it is necessary to inflate the tire virtually by trial and error and to take readings of the pressure frequently.
The operator therefore must be attentive during inflation to see to it that the desired pressure has not been reached, failing that other steps have to be taken to readjust for overpressure.
In U.S. Pat. No. 1,394,494 an air pump is disclosed including a safety valve which, in response to a pressure exceeding a pressure preselected by an adjustable spring, is urged to its open position. In this construction the safety valve is not readily accessible from outside the pump and it therefore requires dismounting, should the pressure exerted by the adjustable spring need to be changed.
It is thus immediately apparent that such an arrangement is inapplicable to hand bicycle pumps owing to the fact that tires must be inflated to different pressures as recommended by manufacturers.
U.S. Pat. No. 1,455,646 discloses an air pump which is manually operable but which is of an entirely different variety than the compact cylindrical bicycle pumps which are adapted to be carried on a bicycle frame. This patent discloses a means for setting the desired pressure to which an inflatable body is to be blown up but the means are not at all adapted to the pumps of the foregoing variety.